1. Field of the Invention
This invention relates to the fabrication of semiconductor integrated circuit structures and in particular to the fabrication of the terminal metallurgy required on the surface of such semiconductor structures.
2. Description of the Prior Art
In the semiconductor art terminal metallurgy is usually produced using the so-called lift-off processes, wherein a uniform layer of the terminal metal is laid down over the entire surface of the chip which is coated by a soluble polymer in those places the metal is not to contact the surface of the chip so that by the dissolution of the polymer the metal in the unwanted areas is lifted off the surface of the chip.
Typical lift-off processes are shown in a number of prior art patents, such as for example, U.S. Pat. Nos. 4,532,002; 4,108,717 and 4,045,594. In these processes metal deposited on the surface of a semiconductor device is lifted off by a dissolving of the underlying organic material.
An improvement to the basic lift-off concept was described in U.S. Pat. No. 4,519,872 which sets forth a lift-off process in which the underlying polymer is thermally depolymerized such that its dissolution can be more quickly accomplished since depolymerized polymer is more easily removed in a solvent.
Another improved lift-off process is described in U.S. Pat. No. 4,428,796 in which the polymer is heated to break the bond between deposited metal and the polymer.
Still another improved lift-off process is in U.S. Pat. No. 4,448,636 which describes a process in which the underlying polymer is heated with radiant energy, such as from a laser, to cause the polymer, under the metal film, to outgass thereby breaking the mechanical bond between the metal film and the resist.